The present invention relates to a pattern test apparatus in which pattern information given by predetermined values such as model patterns of designed data (numerical values) or a photomask used for forming patterns, is reformed or modified, and more particularly, the invention relates to the formation of a loosened reference pattern which is analogous to a practical pattern as a test target.
As the result of treatment, such as exposure, etching or the like, the practical pattern as a target of the test often has its corner portion rounded or often has its line width changed compared with the model pattern as a standard of the test. In the case where the normality of the test pattern is judged from the comparison between the test pattern and the model pattern, if the model pattern without modification is used as a reference pattern, the test pattern may be misjudged to be a poor test pattern though it is so normal that the round of its corner portion or the change of its line width is permissible.
In order to solve the aforementioned problem, in the prior art, the following picture image processing is applied to the model pattern for the purpose of correcting the difference between the model pattern and the practical test pattern to thereby form a processed pattern analogous to the test pattern, as disclosed in JP-A-60-113102.
The prior art picture image processing method is described with reference to the drawing. The method comprises the steps of: calculating the sum value S of the contents (each of which takes the value of "1" when it is contained in a model pattern 24 and each of which takes the value of "0" when it is not contained in the model pattern 24) of outer picture elements as shown by the oblique lines of FIG. 1 in an arrangement 21 of N.times.N picture elements including a picture element 23 located in a corner portion of a model pattern 24 as the center thereof; comparing the sum value S with at least one predetermined value K; and modifying the content X of the center 23 of the arrangement 21 of N.times.N picture elements on the basis of the result of the comparison. In the prior art, the model pattern, as to its corner portion and its line portion, is reformed to be analogous to the practical test pattern by use of the aforementioned method.
In FIG. 1, the inside portion surrounded by the thick solid line to thereby determine the model pattern 24 takes the value of "1", and the outside portion takes the value of "0". If the condition that the center picture element 23 is decided to be "0" when S&lt;K is given (N=5, K=6, S=5), the content of the center picture element 23 is changed from "1" to "0" so that the model pattern 24 is modified to a pattern in which one picture element 23 at its corner has been lost.
The aforementioned prior art technique has been proposed for the purpose of comparison test between a designed data pattern having its corner portion to form a right angle as shown in FIG. 2A and a test target pattern having its corner portion in which one picture element has been lost as shown in FIG. 2B. However, there has been no consideration about a model pattern having its corner portion rounded over several picture elements as shown in FIG. 2C.
Let the prior art technique be applied to the model pattern of FIG. 2C in the condition of N=5, and let the content X of the center be "0" when the sum value S is more than the predetermined value K. If K is any one of the values 1-7, the corner portion cannot be detected. If K is 8, the corner portion is deformed because the two contents of the picture elements 41-a and 41-b are "0". If K is any one of the values 9-16, the corner portion of the pattern cannot be distinguished from the line portion thereof making processing impossible. Consequently, there is no condition for reforming the model pattern of FIG. 2C suitably. Although the aforementioned problem arises in the case of N=5, the same problem also arises in the other cases.
Because the original purpose of the designed data is to generate a desired pattern on the target objects, the corner portion of the designed data may be rounded over several picture elements corresponding to the desired pattern. Accordingly, it is difficult to reform the model pattern to be analogous to the test target pattern by the prior art technique which is merely applied to the corner portion. Therefore, according to the prior art technique, misjudgment by the test apparatus increases.
Further, in the practical etching process, the convex corner A51 of the model pattern must be compressed as the convex corner B52 of the test target pattern as shown in FIG. 3A, whereas the concave corner C53 of the model pattern must be expanded as the concave corner D54 of the test target pattern. However, it is theoretically impossible to process the two patterns at once in the prior art technique.